Microwave strip transmission line circulator

ABSTRACT

A microwave strip transmission line circulator is disclosed comprising at least one body of ferrite material, a ground plane member overlaying one surface of the ferrite body, and a conductive disk overlaying another surface of the ferrite body. At least three strip transmission line conductors extend radially from the periphery of the conductive disk with the axes of the transmission line conductors defining equal angles. The conductive disk has at least three sets of indentations with each set comprising two convergent indentations extending from the periphery of the disk to two juxtaposed lines located substantially equidistant from and along opposite sides of one of said axes. Means are also provided for magnetizing the body of ferrite material.

United States Patent Hartz et a].

[151 3,636,479 [451 Jan. 18, 1972 Claude A. S. Hamrick ABSTRACT Amicrowave strip transmission line circulator is disclosed comprising atleast one body of ferrite material, a ground plane member overlaying onesurface of the ferrite body, and a conductive disk overlaying anothersurface of the ferrite body. At least three strip transmission lineconductors extend radially from the periphery of the conductive diskwith the axes of the transmission line conductors def ning equal angles.The conductive disk has at least three sets of indentations with eachset comprising two convergent indentations extending from the peripheryof the disk to two juxtaposed lines located substantially equidistantfrom and along opposite sides of one of said axes. Means are alsoprovided for magnetizing the body of ferrite material.

5 Claims, 2 Drawing Figures PATENTEU JAN 1 8 I972 INVENTORS NORMAN HARTZBRUCE K. HORNE BY WJJM ATTORNEY MICROWAVE STRIP TRANSMISSION LINECIRCULATOR BACKGROUND OF THE INVENTION This invention relates generallyto fen'ite circulators, and particularly to microwave strip transmissionline type ferrite circulators.

Circulators, as used herein, are N port microwave devices where N isgreater than 2. It has the property that when the ports are suitablynumbered 1 through N an applied input electrical signal at port 1emerges from port 2 with a minimum of attenuation while negligible poweremerges from the other ports. Likewise, a signal applied to port 2emerges from port 3 and so forth.

Microwave strip transmission line circulators of the prior art, such asthose disclosed in US. Pat. Nos. 3,063,024 and 3,359,510, have typicallyemployed a pair of ground plane conductors and a center conductor of thestripline type electrically connected to three ports. Ferrite disks aredisposed between the center conductor and the ground plane conductorsalthough in some types only one ferrite disk is disposed between asingle ground plane conductor and the center conductor. In many casesdielectric disks are placed about the ferrite disks for impedancematching purposes. In both types, however, means are provided forapplying a magnetic field having a strength above or below that whichwould impart ferrimagnetic resonance at the applied microwave frequencyfor the given geometry of the ferrite disk.

In such circulators the ferrite disks act as nonreciprocal perturbativeelements. The dimensions of the disk or ferritedielectric diskassemblies are such that their radii are approximately equal to anintegral number of quarter wavelengths of the operating frequency of thecirculator. In addition, the ferrite disks also act as resonant cavitiesin which electric energy is stored in the capacitance between thestripline center conductor and the ground plane, and magnetic energy isstored in the magnetic fields within the ferrite. A DC magnetic field offixed intensity is established within the ferrite in a directionperpendicular to the stripline center conductor and to the ground planemembers. This perpendicular magnetic field causes the permeability ofthe ferrite to become anisotropic which in turn causing the electricalcoupling between the ports to be nonreciprocal. The dimensions of theferrite disk or disk assemblies determines the resonant frequency of thecavities which, in turn, determine the operating frequency of thecirculator. This results in a dependence between circulator diameter,operating frequency and usable bandwidth.

Today circulators find extensive application in the lower range ofmicrowave frequencies such as 50 to 5,000 MHz. As stated above theoperating frequency of the device determines the size of the ferritedisk and, in turn, the size of the circulator itself which, for suchfrequencies, becomes quite large such as several inches in diameter. Atypical microwave strip transmission line circulator designed to operateat 150 MHz., for example, has a diameter of some 8 inches. Suchrelatively large sizes are costly and present space utilization problemsfor the user.

In 1966 U.S. Pat. No. 3,286,201 issued which was directed towardssolving the aforestated problem through the use of lumped constantelements in the form of mutually coupled coils coupled to the ferrite.Though such lumped constant circulators were highly successful indecreasing the required size of circulators for given operatingfrequencies they were less successful in reducing their costs. This wasoccasioned by the relatively high amount of manual labor required inassembling the lumped constant elements as opposed to that required inassembling distributed constant elements into the circulators. Inaddition to added cost the use of lumped elements introduced new andlower power limitations.

Accordingly, it is a general object of the present invention to providean improved microwave strip transmission line circulator.

More particularly, it is an object of the present invention to provide arelatively small, microwave strip transmission line circulator for givenoperating frequencies in the microwave frequency ranges. 7

Another object of the invention is to provide a microwave striptransmission line circulator having both relatively small size for givenoperating microwave frequencies, and relatively high power handlingcapabilities.

Yet another object of the invention is to provide an inexpensivemicrowave strip transmission line circulator having a relative broadbandwidth.

SUMMARY OF THE INVENTION Briefly described, the present invention is amicrowave strip transmission line circulator comprising at least onebody of ferrite material, a ground plane member overlaying one surfaceof the ferrite body, and a conductive disk overlaying another surface ofthe ferrite body. At least three strip trans mission line conductorsextend radially from the periphery of the conductive disk with the axesof the transmission lineconductors defining equal angles. The conductivedisk has at least. three sets of indentations with each set comprisingtwo convergent indentations extending from the periphery of the disk totwo juxtaposed lines located substantially equidistant from and alongopposite sides of one of the axes. Means are also provided formagnetizing the body of ferrite material.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of one embodimentof a circulator incorporating principles of the present invention, alarge section of which is shown broken away to reveal internal elements.

FIG. 2 is a cross-sectional view of the embodiment of FIG. 1 cut alongline 2--2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail tothe drawing there is shown a microwave strip transmission linecirculator comprising an aluminum casing 10 through which three coaxialconnecting ports 11, 12 and 13 extend. Each coaxial connecting port hasa center conductor 14 which extends through port flange 15. The ends ofcenter conductors 14 are soldered to stripline tabs 16 which areextensions of strip transmission line conductors 17. The threeconductors 17 extend radially from the periphery of conductive disk 20which is coaxially sandwiched between two ferrite disks 22 offerrimagnetic oxide having approximately the same diameter as that ofdisk 20. Conductive disk 20 has three sets of indentations each set ofwhich comprises two V-shaped indentations having two communicatingstriplike legs 24 and 25. Legs 24 in each set extend from the periphery26 of disk 20 to two juxtaposed lines 27. Lines 27 are locatedsubstantially equidistant from axes 18 of strip transmission lineconductors 17 and at least partially define one boundary of legs 25which extend substantially parallel to axes 18.

The two fen'ite disks 22 are sandwiched between two steel pole pieces 30and permanent magnets 31 which are housed centrally within ground planemembers 32 and 33. As pole pieces 30 are electrically as well asmagnetically conductive they also function as ground planes in additionto such functioning by members 32 and 33. Finally, steel shunts 34envelope the permanent magnets and. ground plane members by lining theinside surfaces of aluminum casing 10.

The ferrite disks may have a diameter either larger or smaller than thatof disk 20. However, the diameter of the ferrite disks should be atleast sufficiently large to extend to the nearest approach of legs 24and 25 to the center of disk 20. Such minimum size of the ferrite disksis delineated by are 35. In addition the disks do not have to becircular structures nor have uniform radius. Those portions of periphery26 of conductive disk 20 connecting any two legs 24 in any one set ofindentations, for example, could differ in radius somewhat from thatportion of periphery 26 connecting two adjacent legs of two independentsets of indentations.

A complete understanding of the manner in which the just describedcirculator functions in achieving the aforestated objects of theinvention has not yet been obtained. However, it is believed to beprimarily attributable to the presence of the described indentations.These indentations evidently break disk 20 up into spaced elements whichextend both laterally from the direction of electron flow in each of thethree transmission lines and radially from the center of the diskinbetween such directions of electron flow. These spaced elements ineffect act partially as lumped and partially as distributed constantelements in relation to the ground plane members. Their location interms of input signal wavelength enables them to provide resonantreactances in achieving improved tuning and impedance matching for thesize of the circulator as a whole. Four inch diameter circulators can berealized for successful operation at 150 MHz. through the utilization ofsuch indentations.

it should be understood that the described embodiment is merelyillustrative of application of the principles of the invention and thatmany modifications may be made thereto without a departure from thespirit and scope of the invention as set forth in the following claims.

We claim:

1. A microwave strip transmission line circulator comprising at leastone body of ferrite material; a ground plane 'member overlaying onesurface of said ferrite body; a conductive disk overlaying anothersurface of said ferrite body; at

least three strip transmission line conductors extending radially fromthe periphery of said conductive disk with the axes of said transmissionline conductors defining equal angles; said conductive disk having atleast three sets of indentations with each of said sets comprising twoconvergent indentations extending from the periphery of said disk to twojuxtaposed lines located substantially equidistant from and alongopposite sides of one of said axes; and means for magnetizing said bodyof ferrite material.

2. A microwave strip transmission line circulator in accordance withclaim 1 wherein each of said indentations is V- shaped and comprises twocommunicating legs of unequal length.

3. A microwave strip transmission line circulator in accordance withclaim 1 wherein said body of ferrite material is cylindrical and whereinsaid conductive disk overlays said ferrite body in coaxial relationshipthereto.

4. A microwave strip transmission line circulator in accordance withclaim 3 wherein theradius of said cylindrical body of ferrite materialis at least as large as the radius of the circle defined by the closestpoints to the center of said disk to which each of said indentationsextends.

5. A microwave strip transmission line circulator in accordance withclaim 3 wherein the radius of said cylindrical body of ferrite materialis as least as large as the radius of said conductive disk.

1. A microwave strip transmission line circulator comprising at leastone body of ferrite material; a ground plane member overlaying onesurface of said ferrite body; a conductive disk overlaying anothersurface of said ferrite body; at least three strip transmission lineconductors extending radially from the periphery of said conductive diskwith the axes of said transmission line conductors defining equalangles; said conductive disk having at least three sets of indentationswith each of said sets comprising two convergent indentations extendingfrom the periphery of said disk to two juxtaposed lines locatedsubstantially equidistant from and along opposite sides of one of saidaxes; and means for magnetizing said body of ferrite material.
 2. Amicrowave strip transmission line circulator in accordance with claim 1wherein each of said indentations is V-shaped and comprises twocommunicating legs of unequal length.
 3. A microwave strip transmissionline circulator in accordance with claim 1 wherein said body of ferritematerial is cylindrical and wherein said conductive disk overlays saidferrite body in coaxial relationship thereto.
 4. A microwave striptransmission line circulator in accordance with claim 3 wherein theradius of said cylindrical body of ferrite material is at least as largeas the radius of the circlE defined by the closest points to the centerof said disk to which each of said indentations extends.
 5. A microwavestrip transmission line circulator in accordance with claim 3 whereinthe radius of said cylindrical body of ferrite material is as least aslarge as the radius of said conductive disk.